The measurement of light absorbed by or emitted from a sample can provide a useful measurement of chemical and biological systems and changes occurring therein. For example the determination of the output of light from a sample containing luminescent microorganisms provides a highly sensitive technique for observing the effect of a substance on the metabolism of the microorganism. In carrying out such procedures it is important that the sample be disturbed as little as possible during the light measurement process in order to prevent undesirable fluctuation in the light signal from the sample. Likewise it is important, particularly when the sample involves living organisms, to control the sample temperature as light output can be highly temperature sensitive.
As is conventional in the art, the light output from a sample, be it light from an external light source passing through the sample or light generated from the sample itself, is directed from the sample to a photosensitive device which produces a signal responsive to the intensity of the light impinging thereon. The signal is passed by known circuitry to a readout device such as a meter or recorder. In order to provide efficient utilization of light, the sample and photosensitive device are mounted in close proximity to each other and to the light source, if one is required. Maximum compactness is obtained with instruments employing the so-called "Turret" design reaction chamber such as disclosed in U.S. Pat. No. 3,764,214 (Heiss). However such devices require movement of the sample during the opening and closing of the shutter in the operation of the instrument.
As already mentioned, many luminescent reactions, particularly bioluminescence, are highly temperature sensitive and temperature control of the sample during luminescence measuring operations is important for consistent, reproducible results. Conventional instrumentation, including Heiss, require that a large body mass of the instrument be cooled or heated if control of the sample temperature is desired.